The present disclosure generally relates to apparatus and systems for fuel passages within gas turbine engines, and more particularly relates to apparatus and systems for fuel passages that reduce flow variation due to rust and debris within a fuel supply.
Gas turbine engines include a compressor, a combustor, and a turbine. The compressor creates compressed air, which is supplied to the combustor. The combustor combusts the compressed air with fuel to generate an air-fuel mixture, which is supplied to the turbine. The turbine extracts energy from the air-fuel mixture to drive a load. In many cases, the gas turbine includes a number of combustors. The combustors may be positioned between the compressor and the turbine. For example, the compressor and the turbine may be aligned along a common axis, and the combustors may be positioned between the compressor and the turbine at an entrance to the turbine, in a circular array about the common axis. In operation, air from the compressor may travel into the turbine through one of the combustors.
The combustors may be operated at a relatively high temperature to ensure the mixture of air and fuel is adequately combusted, improving efficiency. One problem with operating the combustors at a high temperature is that a relatively high level of nitrogen oxides (NOx) may be generated, which may have a negative impact on the environment.
To reduce NOx emissions, many modern gas turbines employ fuel nozzles. For example, each combustor may be supported by a number of fuel nozzles, which may be positioned in a circular array about the combustor. During normal operation, the air from the compressor enters the combustor via the fuel nozzles. Within the fuel nozzles the air is mixed with fuel to form an air-fuel mixture. The air-fuel mixture is then combusted in the combustor. Pre-mixing the air and fuel permits operating the combustors at relatively lower temperatures, which reduces the NOx produced as a by-product of the combustion process.
To achieve further performance advantages, many combustors employ fuel injectors that are positioned upstream of the fuel nozzles. One such system, for example, is a fuel injector that is integrated within the combustor casing, which may be referred to herein as a combustor casing fuel injector. This type of fuel injector may be referred to as an annular quaternary fuel distributor. As described in more detail below, this type of system injects fuel into the compressed air discharged by the compressor as this flow of air moves toward the fuel nozzles. In certain cases, as described in more detail below, the combustor casing fuel injector injects fuel into an annulus passageway that is defined by the combustor casing and the cap assembly. It will be appreciated by one of ordinary skill in the art that pre-mixing fuel in this manner may be employed to mitigate combustor instability, to provide better fuel/air mixing, improve flame holding margin of the downstream fuel nozzles, as well as to reduce NOx emissions.
However, combustor casing fuel injectors present their own problems. Typically, in such systems, fuel is delivered into the combustion system by flowing from the gas manifold into an annulus that is integral to the combustion casing. From there the fuel flows down individual peg injectors or pegs that protrude into the air flow stream (i.e., into the annulus passageway that is defined between the combustor casing and the cap assembly). The fuel of the combustor casing fuel injector then is injected into the flowstream via small holes (˜0.05″) that are positioned along the peg injectors. It will be appreciated that this fuel mixes with the flow of compressed air and, downstream, is combusted within the burning zone or combustion chamber of the combustor.
In order meet cost objectives, the annular fuel manifold of the combustor casing fuel injector is constructed as an integral component of the combustor casing. As such, the annular fuel manifold is made of carbon steel, which, over time, means that rust will develop within this fuel passageway. Liberated rust pieces or other debris within the supply of fuel flow down into the pegs and cause a blockage, which may block fuel from flowing into the pegs, flowing through the pegs, or exiting the pegs through the injection holes. It will be appreciated that such blocked may lead to performance issues, such as less efficient engine operation, flame holding, emission problems, etc.
One solution, calls for the combustor casing fuel manifold to be made from materials that will not rust, such as Inco 625 alloy. This, however, raises costs considerably. Coatings that prevent rust also have been tested; however, as of yet, these have not proven successful. Accordingly, there is a need for apparatus and systems that effectively prevent rust and other debris from clogging combustor casing fuel injectors, while remaining cost-effective in application.